Structural color filters based on an all-dielectric metasurface exploiting silicon-rich silicon nitride nanodisks.

An all-dielectric metasurface is deemed to serve a potential platform to demonstrate spectral filters. Silicon-rich silicon nitride (SRN), which contains a relatively large portion of silicon, can exhibit higher refractive indices, when compared to silicon nitride. Meanwhile, the extinction coefficient of SRN is smaller than that of hydrogenated amorphous silicon, leading to reduced absorption loss in the shorter wavelength. SRN is therefore recommended as a scattering element from the perspective of realizing all-dielectric metasurfaces. In this work, we propose and embody a suite of highly efficient structural color filters, capitalizing on a dielectric metasurface that consists of a two-dimensional array of SRN nanodisks that are embedded in a polymeric layer. The SRN nanodisks may support the electric dipole (ED) and magnetic dipole (MD) resonances via Mie scattering, thereby leading to appropriate spectral filtering characteristics. The ED and MD are identified from field profile observation with the assistance of finite-difference time-domain simulations. The manufactured color filters are observed to produce various colors in both transmission and reflection modes throughout the visible band, giving rise to a high transmission of around 90% in the off-resonance region and a reflection ranging up to 60%. A variety of colors can be realized by tuning the resonance by adjusting the structural parameters such as the period, diameter, and height of the SRN nanodisks. The spectral position of resonances might be flexibly tuned by tailoring the polymer surrounding the SRN nanodisks. It is anticipated that the proposed coloring devices will be actively used for color displays, imaging devices, and photorealistic color printing.

Highly transmissive subtractive color filters based on an all-dielectric metasurface incorporating TiO2 nanopillars.

Transmissive subtractive color filters are proposed and demonstrated that take advantage of an all-dielectric metasurface based on a lattice of TiO2 nanopillars (NPs), rendering a high transmission efficiency that exceeds 90%. TiO2 NP elements have been created that exhibit a high aspect ratio. Specifically, a series of lithographic processes are conducted to form a narrow and deep hole in the photoresist, which is accompanied by atomic layer deposition of TiO2. A broad palette of vivid colors encompassing the visible band has been obtained by adjusting the NP diameter for a constant duty ratio of 0.35. For the NP resonator, the electric and magnetic field profiles in conjunction with the scattering cross-sections have been meticulously investigated to theoretically validate that the resonant transmission dips are primarily governed by the simultaneous excitation of an electric dipole and a magnetic dipole via Mie scattering.

Nearly Perfect Transmissive Subtractive Coloration through the Spectral Amplification of Mie Scattering and Lattice Resonance.

Silicon has been utilized in metasurfaces to produce structural color filters due to its compatibility with mature and cost-effective methods for complementary metal oxide semiconductor devices. In this work, we propose and demonstrate efficiency- and scattering-enhanced structural color filters using all-dielectric metasurfaces made up of engineered hydrogenated amorphous silicon (a-Si:H) nanoblocks. Wavelength-dependent filtering is achieved by Mie scattering as each structure individually supports the electric dipole (ED) and magnetic dipole (MD) resonances. The ED and MD resonances are identified by observing the field profiles of the resonance calculated by finite element method (FEM) simulations. To enhance the efficiency and scattering response of the all-dielectric metasurfaces, the proposed structural color filters are designed with consideration of the lattice resonances and scattering directivity. The spectral positions of the transmission dips and peaks are rigorously analyzed in accordance with the Mie theory and multipole expansion. The transmission spectra exhibit 100% transmission where Kerker's first condition is satisfied, while the lattice resonances amplify the ED and MD scattering responses throughout the entire visible regime. Various colors are generated by varying the resonance peak, which is controlled by varying the geometric parameters of a-Si:H nanoblocks. The proposed structural color printing devices are expected to have applications in dynamic color displays, imaging devices, and photorealistic color printing.

Polarization-Controlled Broad Color Palette Based on an Ultrathin One-Dimensional Resonant Grating Structure.

Highly efficient polarization-tuned structural color filters, which are based on a one- dimensional resonant aluminum grating that is integrated with a silicon nitride waveguide, are proposed and demonstrated to feature a broad color palette. For such a metallic grating structure, transmissive color filtering is only feasible for the incident transverse-magnetic (TM) polarization due to its high reflection regarding the transverse-electric (TE) case; however, polarization-tuned customized colors can be efficiently achieved by optimizing the structural parameters like the duty ratio of the metallic grating. For the fabricated color filters, the transmission peaks, which are imputed to the resonance between the incident light and the guided modes that are supported by the dielectric waveguide, provided efficiencies as high as 90% and 70% for the TM and TE polarizations, respectively, as intended. Through the tailoring of the polarization, a group of filters with different grating periods were successfully exploited to produce a broad color palette spanning the entire visible band. Lastly, a nanoscale alphabetic pattern featuring a flexible combination of colorations was practically constructed via an arrangement of horizontal and vertical gratings.

All Dielectric Transmissive Structural Multicolor Pixel Incorporating a Resonant Grating in Hydrogenated Amorphous Silicon.

All dielectric transmissive type polarization-tuned structural multicolor pixels (MCPs) are proposed and demonstrated based on a one-dimensional hydrogenated amorphous silicon (a-Si:H) grating integrated with a silicon nitride waveguide. Both bandpass and bandstop transmission filtering characteristics in the visible regime, centered at the same wavelength, have been achieved by tailoring the structural parameters including the duty ratio of the grating and the thickness of the dielectric waveguide. For the three manufactured MCPs, the transmission peak exceeds 70% for the transverse electric (TE) polarization and 90% for the transverse magnetic (TM) polarization as observed at the resonance and off-resonance wavelength, respectively. The polarization-switched transmissions are attributed to the guided mode resonance initiated by the interaction of the a-Si:H grating and the dielectric waveguide. A broad color palette covering the entire visible band was successfully realized from a suite of MCPs with varying grating pitches. The proposed structural color pixels are expected to facilitate the construction of dynamic displays, image sensors, optical data storage, security tags, and so forth.